Yes, you can use your A500 drive in the A4000T. Do it like this:
1) Disconnect the floppy drive cable from the small PCB that is attached to the disks module. Remove that small PCB.
2) Plug the floppy cable directly to the header where the PCB was plugged previously.
3) Replace the A4000T drive with the A500 drive.
I can vouch that this works, because I recently did quite a few experiments with floppy drives and my A4000T and PC.